The research proposed here is an investigation of the mechanisms by which early development is initiated. Much of what is known about these mechanisms has been learned from study of sea urchin embryos in which fertilization causes a dramatic activation of egg metabolism. However, there is reason to expect that such a dramatic metabolic activation should not occur in most animals, including mammals, because their oocytes are metabolically active before fertilization. The aim of this research, therefore, is to examine the activation program in a species in which the egg is metabolically active before fertilization. Eggs of the parchment worm, Chaetopterus pergamentaceus, will be used because they offer nearly all of the technical and experimental advantages of sea urchin eggs, with few of the disadvantages. Our primary series of experiments will test whether intracellular signals involved in the activation of sea urchin eggs, specifically increased intracellular calcium, are involved in the initiation of development in these eggs. This will be tested biochemically by examining the calcium sequestration and release mechanisms active in these eggs. In parallel, using aequorin luminescence and photon imaging, we will also measure calcium fluxes in the eggs during activation both by sperm and by excess KC1. The results of these studies will provide a direct and unambiguous test of whether or not the activation program of sea urchin eggs is broadly applicable. Since the criteria used for egg activation in this species (meiotic cell division and cellular rearrangements characteristic of differentiation without cleavage) are directly relevant to the initiation of development (unlike the cortical reaction in sea urchins which is often given as the criterion for activation), results of these studies should have relevance for mechanisms initiating the development of all organisms. The results will therefore have relevance to the understanding and management of fertility and birth defects. Because the program of fertilization initiates cell division, they also will have relevance to the general understanding of the control of cell division and to the management of abnormal cell division in cancer.